The present invention relates to computing systems formed of one or more arrays of interconnected hardware modules. More particularly, the present invention relates to a digital computer system in which its capacity and fault tolerance are determined by the number and arrangement of modular hardware elements installed in and thereby connected in one or more receptacle arrays. Robotic installation and removal of modules in the environment of the arrays is an aspect of the present invention.
The assignee of the present invention has pioneered the concept of fault tolerance in connection with computing system. Basically, that concept holds that failure of one element or subsystem of a computing system should never be permitted to cause the whole system to fail. In practice, the use of parallel processors, parallel data paths to peripheral equipment and parallel power supplies has resulted in a fault tolerant computing system which has significantly advanced the art. This advance is documented, for example, in U.S. Pat. No. 4,228,496, the disclosure of which is incorporated herein by reference.
In practice, discrete hardware elements of a computer, such as processors, peripheral device controllers, central memory, data mass storage devices, and power supplies are formed as separate hardware elements, and these elements are typically interconnected by cabling, and sometimes by direct plug in connection to back planes or mother boards.
On commonly encountered hardware element is the rotating data storage device, sometimes called "disk drive". Disk drives, whether based on magnetic or optical storage technologies, are frequently used in computing systems to provide rapid, random access to stored data. Over the years, disk drive technology has progressed to a point where a massive amount of data may now be stored in a disk drive device using small diameter non-removable disks (e.g. eight inch) and having a very small physical package.
Heretofore, the servicing of existing digital computer systems, including systems practicing fault tolerance, has involved the disconnection of cables and harnesses interconnecting the various subsystems such as disk drives. Such servicing has typically included the removal and reinstallation of cabinetry and mounting hardware. Because of the way in which prior computering systems have been designed, constructed and assembled, removal of a circuit board or a cable during servicing has either required that all primary power to the subsystem be removed or has led to failure of backup or mirror subsystems, causing a single point failure within the computing system.
Also, the manner in which computing systems have been assembled has not been conducive of automatic maintenance procedures. While industrial robots are known and widely employed in industrial manufacturing processes, little if any effort has been given to the adaptation of computing systems and programmed robotic equipment to facilitate automatic maintenance procedures.
Thus, a hitherto unsolved need has arisen for a fault tolerant digital computer incorporating subsystems and hardware elements thereof which may be serviced, either manually or automatically by robotic maintenance equipment, without disturbance of the cabinet and cabling housing and connecting the disk drive to be serviced.